1. Field of the Invention
The present invention generally relates to an illuminating device for vehicles, which is suitable to be used as a headlamp of vehicles or the like.
2. Description of Related Art
Regarding an illuminating device for vehicles, it is generally known a device as shown by FIG. 9, for example, in which light emitted from a light source is introduced into one end of an optical fibre and the incident light is guided through the optical fibre so as to be emitted from a light conducting path lens provided at the other end of the optical fibre. In other words, in FIG. 9, the illuminating device for a vehicle comprises a light: source 10 disposed at the center of front part of a vehicle and a pair of headlamps L and R disposed symmetrically with respect to the light source 10. The light source 10 has an approximately cylindrical casing 11 in which a discharge lamp 12 is disposed at the center of axial direction as a linear or line light source.
Further, each of left side elliptical mirrors 11La through 11Ld and each of right side elliptical mirrors 11Ra through 11Rd are formed symmetrically in the sidewise direction over the internal peripheral wall of the casing 11. Then, light released from the discharge lamp 12 is reflected by the right side elliptical mirror 11Ra and each of left side elliptical mirrors 11Lb through 11Ld and condensed at the center of right side wall 11b of the casing 11 while, at the same time, the light is reflected by the left side elliptical mirror 11La and each of left side elliptical mirrors 11Rb through 11Rd and each of right side elliptical mirrors 11Ra through 11Rd and condensed at the center of left side wall 11a of the casing 11.
The left headlamp L comprises a light conducting path lens 20 provided at the left front part of the vehicle and an optical fibre 30 connecting between the light conducting path lens 20 and the light source 10. On the other hand, the right headlamp R comprises a light conducting path lens 40 provided at the right front part of the vehicle and an optical fibre 50 connecting between the light conducting path lens 40 and the light source 10. The light conducting path lens is as illustrated in FIG. 10 and FIG. 11A, and, as shown by FIG. 12A, cross sectional shape of the light conducting path lens 20, which is cut out in X-Y plane, is approximately trapezoidal while cross sectional shape which is cut out in X-Z plane, resembles approximately a fan or an arc shape.
However, in the construction as described above, if the shape projected from the optical fibre 30 onto incident light plane 22 of the light conducting path lens 20 is a disc as shown by FIG. 11A, when the incident light from the optical fibre 30 onto the light conducting path lens 20 progresses while being reflected on reflection planes 23 and 24, and emits from outgoing light plane 21, images projected from the optical fibre 30 onto the incident light plane 22 of light conducting lens 20 appear equivalent to the number of reflections on the reflection planes 23 and 24. In the case, if the shape of optical fibre 30 is projected straightly onto the incident light plane 22, a bright part A in a disc and a bright part A' in a neighboring disc do not become continuous as shown by FIG. 11B and consequently a problem of incoherent brightness caused by the bright part A in the disc and a dark section B outside the disc results.
Further, as shown by FIG. 12A, if a reflection on the reflection plane 23 is considered, when the incident light emitted from the optical fibre 30 and entering in the light conducting path lens 20 progresses while being reflected by the reflection planes 23 and 24 and emits from the outgoing light plane 21, since tilts of the perpendicular line n on the outgoing light plane 21 and the perpendicular line n' on an imaginary outgoing light plane 21' are not coincidental at a point P, direct outgoing light 1 and outgoing light 1' after reflection do not become continuous and thus, as shown by FIG. 12B, the bright part A in the disc and the bright part A' in the neighboring disc do not become continuous so that a problem of incoherent brightness consisting of bright parts A and A' in the discs and a dark part B out of the discs results.